Hydroacoustics is a general term for the study and application of sound in water. The term comes from Greek υδρο, water, and ακουστική, acoustics. Hydroacoustics, utilizing SONAR technology, is most commonly used for detection, assessment, and monitoring of underwater physical and biological characteristics.
Hydroacoustics can be utilized to detect the depth of a water body (bathymetry), as well as the presence or absence, abundance, distribution, size, and behavior of underwater plants and animals. Hydroacoustic sensing involves "passive acoustics" (listening for sounds) or active acoustics making a sound and listening for the echo, hence the common name for the device, echo sounder or echosounder.
There are a number of different causes of noise from shipping. These can be subdivided into those caused by the propeller, those caused by machinery, and those caused by the movement of the hull through the water. The relative importance of these three different categories will depend, amongst other things, on the ship type  One of the main causes of hydro acoustic noise from fully submerged lifting surfaces is the unsteady separated turbulent flow near the surface's trailing edge that produces pressure fluctuations on the surface and unsteady oscillatory flow in the near wake.The relative motion between the surface and the ocean creates a turbulent boundary layer (TBL) that surrounds the surface. The noise is generated by the fluctuating velocity and pressure fields within this TBL.
- Surveillance Towed Array Sensor System
- Fisheries Acoustics
- Acoustic Doppler Current Profiler for water speed measurement
- Acoustic Camera
- Passive Acoustic Monitoring
- Quality assurance of hydroacoustic surveys: the repeatability of fish-abundance and biomass estimates in lakes within and between hydroacoustic systems (free link to document)
- Hydroacoustics as a tool for assessing fish biomass and size distribution associated with discrete shallow water estuarine habitats in Louisiana
- Acoustic assessment of squid stocks
- Summary of the use of hydroacoustics for quantifying the escapement of adult salmonids (Oncorhynchus and Salmo spp.) in rivers. Ransom, B.H., S.V. Johnston, and T.W. Steig. 1998. Presented at International Symposium and Workshop on Management and Ecology of River Fisheries, University of Hull, England, 30 March-3 April 1998
- Multi-frequency acoustic assessment of fisheries and plankton resources. Torkelson,T.C., T.C. Austin, and P.H. Weibe. 1998. Presented at the 135th Meeting of the Acoustical Society of America and the 16th Meeting of the International Congress of Acoustics, Seattle, Washington.
- Acoustics Unpacked A great reference for freshwater hydroacoustics for resource assessment
- Inter-Calibration of Scientific Echosounders in the Great Lakes
- Hydroacoustic Evaluation of Spawning Red Hind Aggregations Along the Coast of Puerto Rico in 2002 and 2003
- Feasibility Assessment of Split-Beam Hydroacoustic Techniques for Monitoring Adult Shortnose Sturgeon in the Delaware River
- Categorising Salmon Migration Behaviour Using Characteristics of Split-beam Acoustic Data
- Evaluation of Methods to Estimate Lake Herring Spawner Abundance in Lake Superior
- Estimating Sockeye Salmon Smolt Flux and Abundance with Side-Looking Sonar
- Herring Research: Using Acoustics to Count Fish.
- Hydroacoustic Applications in Lake, River and Marine environments for study of plankton, fish, vegetation, substrate or seabed classification, and bathymetry.
- Hydroacoustics: Rivers (in: Salmonid Field Protocols Handbook: Chapter 4)
- Hydroacoustics: Lakes and Reservoirs (in: Salmonid Field Protocols Handbook: Chapter 5)
- PAMGUARD: An Open-Source Software Community Developing Marine Mammal Acoustic Detection and Localisation Software to Benefit the Marine Environment; http://www.pamguard.org/home.shtml
- reducing underwater noise pollution from large commercial vessels